Replies per Help-Desk Ticket

Problem

Table: `Messages`

```text
+-----------+------+
| Column | Type |
+-----------+------+
| msg_id | int |
| root_id | int |
+-----------+------+
There is no single primary key; the same msg_id may appear more than once.
A message with root_id = NULL is a brand-new ticket. A message with a
non-NULL root_id is a reply, and root_id is the msg_id of the ticket it
replies to.
```

For each ticket (a message whose `root_id` is NULL), report how many distinct replies it has. A reply counts once even if its `msg_id` appears multiple times. A reply whose `root_id` does not match any ticket is ignored.

Return `ticket_id` and `reply_count`, ordered by `ticket_id` ascending.

Tables

Example rows — the live problem includes the full dataset.

Expected output

Your answer should return 3 rows with the columns ticket_id, reply_count.

Starter code (SQL)

SELECT *
FROM Messages;

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